Preheat grill to medium-high.

Cook bacon until almost done but not crisp; drain on paper towels.

Curl each shrimp and wrap in a slice of bacon. Assemble skewers: thread 1 bacon-wrapped shrimp, 1 mushroom half, 1 piece bell pepper, 1 piece pineapple; repeat, ending with bacon-wrapped shrimp.

Combine olive oil, lemon juice, catsup, and brown sugar in a small saucepan; place over medium heat and cook, stirring, until brown sugar completely dissolves.

Baste skewers with sauce; place on grill and cook, turning and basting, until shrimp are opaque and bacon crisps.(Bacon fat may cause fire to flare up. Be ready with a spray bottle of water.) Serve at once.