Preheat grill or broiler.
To prepare red onion marmalade:
Place chopped red onions, Lambrusco, orange juice and sugar in a saucepan and place over medium high heat. Bring to a boil, lower heat to medium and reduce until thick like marmalade, about 30 minutes. Remove from heat and allow to cool. Yield: 1 cup
Place Pancetta slices on grill and cook until golden brown, about 4 to 5 minutes per side, and remove to a cutting board. Grill bread slices until golden brown and remove to serving platter. Smear 3 tablespoons red onion marmalade on each slice of bread. Chop warm Pancetta into 1/4-inch cubes and divide among the 4 pieces of bread and serve immediately.