Heat 2 tablespoons olive oil in a large pot over high heat.
Add the diced onion and red pepper and cook 3–5 minutes until the onion is translucent, then push the vegetables to the sides of the pot.
Add the ground beef to the center of the pot and sear about 1 minute per side, then break it up with a wooden spoon and cook until mostly browned with a bit of pink remaining.
Stir in the minced garlic, tomato paste, taco seasoning, and beef bouillon powder. Season with salt and pepper and cook until the beef is fully browned.
Add the canned diced tomatoes, enchilada sauce, and chicken broth and bring the mixture to a full boil.
Break the spaghetti in half and submerge it in the boiling liquid. Cook 10–12 minutes, stirring often and scraping the bottom to prevent sticking; about 8–10 minutes in, reduce heat to medium if the liquid is evaporating too quickly.
When the pasta is al dente, remove the pot from heat. Toss with tongs for about a minute to let the sauce thicken and finish cooking the pasta.
Allow to cool slightly, then gradually add the shredded cheddar 1/4 cup at a time, tossing until fully incorporated to avoid clumping.
Serve immediately.