Preheat oven to 350 degrees. Coat a 9x12 inch oblong pan with non-stick cooking spray.
Brown ground beef, then place in a colander to drain fat.
In the same pan, cook onions, then add cooked ground beef, taco seasoning mix, garlic powder, tomato paste and water (half of the empty tomato paste can filled with water). Cook on medium heat, stirring occasionally until well combined and sauce is thickened, about 10 minutes. Season with salt and pepper to taste. Place taco beef in a colander to allow any excess sauce to drain (this will keep crust from getting soggy).
Place crescent roll dough in prepared pan, and spread out with fingers to touch the sides. Press down on perforated edges to close them.
Place drained taco beef on top of dough, then cover with shredded cheese.
Bake for 20 to 25 minutes until cheese is melted and dough is lightly browned.
Cut into squares and top each serving with diced tomatoes and a dollop of sour cream.
Makes 6 generous servings.
VARIATIONS: If desired, you can use light or fat free sour cream for the garnish. You can also substitute cheese with a package of shredded Mexican or Taco flavored cheese if you want.