Heat olive oil over medium-high heat in a 6-quart soup pot. Add onions, jalapenos (if desired), and 2 teaspoons of the salt and cook until soft, 2 minutes. Add ground beef, chili powder, oregano, and garlic and cook, breaking up any clumps of meat with a spoon, for 5 minutes. Add tomatoes, beans, and 1/2 cup of water, stir, and bring chili to a boil. Reduce heat to a simmer and cook until thickened to chili consistency, about 20 minutes. Taste and add 1 more teaspoon salt, if needed.

Preheat oven to 400 degrees F.

While the chili is simmering, cook macaroni according to package directions in boiling salted water, drain in a colander, rinse under cool running water and set aside. Grate cheddar cheese and set aside.

Place a 9 x 13.5-inch or other 3-quart casserole dish on a baking sheet. Once chili has finished cooking, fold in the cooked macaroni and 1/3 of the cheddar cheese. Transfer chili-mac to the baking dish and top with remaining cheese. Bake until heated through and cheese is melted, about 10 minutes. Remove from oven and let cool 5 minutes before serving.

Serve each portion garnished with a dollop of sour cream, if desired.