Any recommendations for a quick lunch (soup and sandwich type or Falafel ) in area around Napoleon's tomb. I know there is a cafeteria somewhere in the complex, but it didn't get very good reviews.

Do I need to go to a bistro or brasserie ? If so, can I order just a sandwich (on a baguette of course) ? I prefer to save my dining experience for dinner.

Also, what is the time frame for serving of lunch ? From 12 to 2, or earlier?

Also, do some restaurants open for dinner as early as 6 pm ?
I appreciate all feedback.

I would have some ribs, so you can rip the bone apart.

You'll see sandwiches for sale all over the place. If you don't want to stop in a café, all of the boulangeries sell them, too.

Regarding early dinners, many places don't open until 7pm for dinner but quite a few brasseries and most chain restaurants will have the indication "service non-stop" or "service continu" which mean that they serve full meals at all hours.

There is Lenôtre Ecole militaire near by if you want a high end picnic lunch. If you are a foodie, except for brasseries, restaurants open at 6 pm would probably not be on your list of places to go.

You really shouldn't need help finding a sandwich in Paris, or for that matter feeding yourself at any time of day or night. Soup might be more problematic, and falafel around Les Invalides is probably not going to happen, but honestly, are you worried about getting fed in, um, Paris? And do you need specific advice about how to do that? Dinner generally starts around 7 pm, but anyplace that advertises service non-stop will have food anytime of day, maybe not good food, though

Almost any boulangerie will have sandwiches for sale.

No regular restaurant serves dinner at that time. The earliest I have seen is 6:30-7, and that's early (I think Bofinger opens at 6:30). Even teh Relais d'Entrecote restaurants, of which I'm a fan, don't open until 7 pm. Some of the bigger cafes that will serve something all the time, will NOT have their special dinner menu yet at that time, either. You could order a sandwich or salad or snack, though.

I am not a foodie, so I will be perfectly happy with a meal in a brasserie. I prefer to spend my time sightseeing, and not waste it dressing up and going to a fancy restaurant for dinner. I just want to have some idea of where to go in certain areas, so I can plan to eat a decent meal.
I don't want to be wandering around looking for any old fast food place at the end of the day, when I'm ravenous.

Thank you all for your advice and suggestions.

You will be surrounded by every level of restaurant, bistro, rasserie, creperie in that area.

I would suggest traveling west from the Invalides towards the Tower. Rue Cler is just a few blocks west, if you like those type of places. I can say we ate at Cafe du Marche on Rue Cler in 2011 and we were pleasantly surprised. The cost was reasonable. Otherwise, hit any of the boulangeries as mentioned above. Rue Saint-Dominique has numerous places, just look at the menu posted outside and see if anything looks reasonable and appetizing. You're in Paris, and you're not a foodie, so you shouldn't have any meal issues.

Rue Saint Dominique is indeed the most "normal" street of this highly overpriced area.