Add the chopped onion, chopped red bell pepper, pinto beans, kidney beans, crushed tomatoes, chili powder, ground cumin, salt, black pepper, and vegetable broth to your slow cooker. Stir well to combine all the ingredients. Make sure everything is thoroughly mixed for even flavor. Cover and cook on high for 4 hours or on low for 6-8 hours, allowing the flavors to meld together and the vegetables to soften.
After the slow cooker has finished its initial cook, stir in the uncooked whole wheat elbow macaroni. Re-cover and continue cooking on high heat for an additional 15-20 minutes, or until the pasta is tender. Once the pasta is cooked through, stir in 1 cup of the shredded cheddar cheese, allowing it to melt into the chili. I like to use Monterey Jack or mozzarella sometimes for a change in flavor and texture.
Serve the chili mac hot, topped with the remaining 1/2 cup of shredded cheddar cheese and a generous sprinkle of chopped green onions. This final touch adds a bright color and fresh flavor. For a more vibrant finish, I like to add extra green onions right before serving.