Heat oil in a small nonstick skillet over medium heat. Add onion and saute until light golden, about 3 minutes. Add garlic, jalapeno and cumin; saute until fragrant, about 2 minutes longer. (If the mixture becomes too dry, add 1 tablespoon water.) Transfer the mixture to a medium bowl.Advertisement
Prepare a grill or preheat the broiler. Add beans to the onion mixture and mash coarsely with a potato masher. Add beef, tomato paste, cilantro, thyme, salt and pepper; mix thoroughly but lightly. Shape the mixture into four 3/4-inch-thick patties (see Tip).
Grill or broil the patties on a lightly oiled rack until browned and cooked through, about 5 minutes per side. Place on rolls and garnish with salsa and lettuce.
When forming burger patties, make them thinner at the center to prevent them from steaming as they cook.
3 starch, 1 vegetable, 3 lean meat