1. Heat a small nonstick skillet over medium-high heat. Coat pan with cooking spray. Add onion to pan; cover and cook 8 minutes or until golden brown, stirring frequently. Remove from heat; set aside.
2. Remove 1 teaspoon adobo sauce from can; set aside. Remove 1 chipotle chile from can; chop and set aside. Reserve remaining chiles and adobo sauce for another use.
3. Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add beef to pan; cook 4 minutes or until browned, stirring to crumble. Add bell pepper to pan; sauté 2 minutes. Stir in chopped chipotle chile, adobo sauce, tomato paste, and next 3 ingredients (through tomato sauce); cook 3 minutes, stirring occasionally. Spoon 1/2 cup beef mixture over bottom half of each bun, and top evenly with onions and top half of bun.
Plate with pickle chips and a simple slaw. Combine 1/3 cup canola-based mayonnaise, 1 1/2 teaspoons sugar, 1/2 teaspoon freshly ground black pepper, 1/4 teaspoon salt, and 1/4 teaspoon dry mustard in a large bowl; stir with a whisk. Add 3 cups packaged cabbage-and-carrot coleslaw, tossing well to combine.