- Heat grill to medium-high.
- Heat oil and butter in large nonstick skillet on medium-high heat. Add onions, salt and pepper; cook for 10 min., or until softened. Add vinegar; cook 2-3 min. or until onions begin to caramelize, and liquid is mostly evaporated. Reduce heat to medium; stir in 2 cups sauce. Remove from heat; cool.
- Meanwhile, grill burger patties 3-4 min. on each side or until cooked through (165°F). Brush both sides of patties with remaining sauce and top with cheese during last 2 min. of cooking. Fill buns with burgers, Tangy Tomato Jam and arugula.
Leftover Tangy Tomato Jam makes a great sandwich spread or crostini topper.
Look for refrigerated plant-based burger patties in the fresh meat section of the supermarket.