According to Cover & Bake (a cookbook from the Cook's Illustrated folks), Chili Mac is a dish that "everyone" grew up with—except me. As far as I can tell, it's American Chop Suey (elbow macaroni with ground meat and tomato sauce) with the addition of chili powder and melted cheese on top.
I tried this recipe one night last week. The kids are still a little weirded out about casserole-style food where everything's touching everything else, but they deemed this "OK." I loved it and will spring it on them again.
1 Tbsp salt
½ lb. elbow macaroni
3 Tbsp vegetable oil, divided use
1½ lb. ground turkey or ground beef
2 medium onions, chopped medium
1 red bell pepper, seeded and chopped medium
6 garlic cloves, pressed
2 Tbsp chili powder
1 Tbsp cumin
1 (14½-oz.) can diced tomatoes, undrained
1 (28-oz.) can tomato puree
1 Tbsp brown sugar
8 oz. Co-Jack (mixture of Colby and Jack) cheese, shredded
Heat oven to 400°. Bring 4 quarts of water to a boil in a Dutch oven. Stir in salt and macaroni and cook until al dente, about 5 minutes. Just before it's done, dip your Pyrex measuring cup in and reserve ¾ cup of the pasta water. Drain the pasta, transfer it to a bowl, and set aside. Don't bother washing the colander yet.
Wipe the Dutch oven dry and set over medium-high heat. Add 1 Tbsp of the oil and heat until shimmering. Add the ground meat and cook, breaking up the pieces with a wooden spoon, until no longer pink and beginning to brown, 5–8 minutes. Drain the meat through the colander, discarding the fat, and set aside.
Add the remaining 2 Tbsp oil to the Dutch oven and return to medium-high heat. When the oil is shimmering, add the onion, red pepper, garlic, chili powder, and cumin. Cook, stirring occasionally, until the vegetables are softened and beginning to brown, about 7 minutes.
Add the diced tomatoes and their juice, tomato puree, brown sugar, reserved pasta water, and drained meat; bring to a simmer. Lower heat and cook for 20 minutes, stirring occasionally, to allow the flavors to meld.
Stir in the cooked pasta and season with salt and pepper to taste. (I didn't bother with the seasoning, figuring–correctly—that the dish was already flavorful enough.) Pour into a 9x13" baking dish and sprinkle with the cheese. Bake until the cheese is melted and browned, about 15 minutes. Cool for 5–10 minutes before serving.