Place lettuce in a large bowl and top with chopped tomato and pickle. Set aside.
Bring a skillet sprayed with nonstick spray to high heat on the stove. Add onion and cook until slightly browned and softened, about 3 minutes. Transfer to the large bowl and set aside.
Prepare Boca patty according to package instructions (either in the microwave or in a skillet sprayed with nonstick spray). Once just cool enough to handle, chop into bite-sized pieces and transfer to a small bowl. Add mustard and toss to coat. Transfer the mustard-y burger bites to the salad bowl. Evenly top salad with cheese and dressing.