Preheat oven to 400°F. Heat a large non-stick pan over medium-high heat. Add Beyond Meat sausage and cook for 5-8 minutes. Set aside. Return pan to medium-high heat with 1 tbsp olive oil. When oil is shimmering, add onion. Cook, stirring frequently, until onion softens, 5-7 minutes. Reduce heat to medium, add balsamic vinegar and cook until vinegar is evaporated and onions are jammy, about 10 more minutes. Top pizza with tomato sauce, mozzarella, sausage, red pepper and balsamic onions, in that order. Bake until cheese is melted, 10-15 minutes.