Step 1 Place chicken into a food processor. Pulse until coarsely chopped, then transfer to a bowl. Add onion, garlic and parsley. Season with pepper. Form mixture into 4 patties.
Step 2 Spray a large frying pan with oil and place over medium-high heat. Cook patties for 4–5 minutes on each side, or until cooked through. Add lemons to pan, cut side down, for last 2 minutes of cooking time.
Step 3 Meanwhile, steam asparagus until just tender. Remove and toss with tomatoes and juice from one lemon half. Place patties on toasted rolls, then top with asparagus and tomatoes. Cut remaining lemon halves into wedges to serve with burgers.