Brown diced bacon 3 to 4 minutes on medium-high heat.
Rinse the salmon and pat dry. Place the salmon skin-side down in a baking pan. Spread mayonnaise evenly over the entire salmon. Place the diced onion, tomato,mushroom and bacon on the fish, then spoon the capers over the filling. Squeeze the juice from half a lemon over the entire fish. You may want to use less juice since capers are also added. Finally, sprinkle some salt and pepper over the fish and stuffing.
Cover the salmon tightly with foil and bake in oven for about 35 to 45 minutes, or until the vegetables are slightly cooked and the fish is tender.
When the fish is done, it will look as if a handful of confetti was thrown on top of it.