Preheat the oven to 300 degrees F.
Lightly wrap the French bread in aluminum foil and place in the oven until warmed, about 10 minutes. Remove from the oven and increase the heat to broil.
Meanwhile, in a large skillet, heat the oil over medium-high heat. Add the onions, and peppers and cook, stirring, until softened and caramelized around the edges, about 6 minutes. Remove from the heat and season with the Essence.
Slice the French bread crosswise into 4 portions, and then cut each piece lengthwise. Spread both cut sides of the bread generously with mayonnaise, and divide the hot meatballs and some of the sauce between the 4 sandwich bottoms. Divide the grated mozzarella and Parmesan between the sandwiches, then top each sandwich with onions and peppers. Top with more of the remaining sauce. Place the bottom of the sandwiches on a baking sheet and broil in the oven until the cheese is melted. Remove from the oven and top with the remaining bread. Serve immediately.
Yield: 4 generous servings