In a 5- to 6-quart pan over medium-high heat, stir ground beef, garlic powder, and 1 teaspoon salt until beef is crumbly and well browned, 6 to 8 minutes.
With a large slotted spoon, push beef mixture to one side of pan and tilt pan so liquid runs to opposite side. Stir flour into liquid until well blended, then mix with beef mixture. Add 2 cups water, black beans if using, and dried chilies; stir until mixture boils and thickens, about 8 minutes.
Spread about 3/4 cup Fritos in each of six wide, shallow bowls and sprinkle chopped onion equally on top. Divide chili equally among bowls and top with cheese, lettuce, and tomato. Add more salt to taste.