In a Dutch oven or large deep skillet, cook the chopped onion and bell pepper in 2 tablespoons of olive oil over medium heat until softened. Add the garlic and cook for another minute until fragrant.
Add the ground beef and break it apart with a wooden spoon. Season with chili powder, cumin, garlic powder, onion powder, ground mustard, dried oregano, thyme, salt, and pepper, and stir to combine. Cook the beef until no longer pink.
Add the beans, tomatoes, tomato paste, and broth, and stir the chili to combine. Season with more salt and pepper to taste. Simmer the chili for about 15 minutes to let the flavors develop. Preheat your oven to 375°F while the chili simmers.
Transfer the chili to a buttered 9 x 13-inch baking dish and neatly place frozen tots on top in a single layer. Bake the casserole uncovered for 25 to 30 minutes, until golden brown and bubbly.
Carefully sprinkle shredded cheddar cheese on top of the casserole and bake for an additional five minutes until the cheese is melted. Garnish the casserole with chopped green onions, cool slightly, and enjoy.