Prepare taco shells. Cook and stir hamburger in 10 inch skillet until light brown; drain. Stir in water, 1/2 cup onion, the chili powder, salt, cumin and garlic. Heat to boiling; reduce heat. Simmer uncovered, stirring occasionally, until thickened, about 10 minutes. Spoon about 1/4 cup hamburger mixture into each taco shell. Top with lettuce, onion, cheese, tomato and sour cream.
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