Cook ground chuck and onion in a large skillet over high heat, stirring until beef crumbles and is no longer pink; drain. Return to skillet; stir in cottage cheese. Set aside.
Process diced tomatoes and tomato sauce in a food processor until smooth, stopping to scrape down sides. Stir in chopped chiles, if desired.
Spoon 2 to 3 tablespoons ground beef mixture down the center of each tortilla; top each with 2 tablespoons tomato mixture and 1 1/2 tablespoons cheese. Roll up tortillas, and place, seam side down, in a lightly greased 13- x 9-inch baking dish. Pour remaining tomato mixture over top; sprinkle with remaining cheese.
Bake enchiladas at 350° for 20 minutes or until bubbly. Garnish, if desired.