Gail, I have been making this recipe for almost 50 years, it doesn't include green pepper but you surely could add it in.
TUNA NOODLE CASSEROLE

8 oz. medium egg noodles
2 cans tuna fish, flaked and well drained
1 can cream of mushroom soup
1/2 soup can of milk
potato chips, the broken up ones toward the end of the bag. Scrunch them up in the bag with your hands till they are fairly small pieces, but not crumbs. You need enough to cover the top of the casserole.

Cook noodles according to package directions, just until there is a little resistance when you bite into one. Drain, no need to blanch with cold water.
Put tuna into a strainer and press out the juice with the back of a spoon.
Spray a 2 qt. round casserole with Pam.
Put soup, milk and tuna in casserole and mix up.
Add cooked and drained noodles, mix all together well.
Spread potato chips on top.
Bake in 350° oven for about 45 minutes, or until bubbly and the chips have browned