Preheat the oven to 450F. Combine the breadcrumbs, parsley and garlic.
Heat 2 tsp oil over medium-high heat in a large skillet.
Add the breadcrumb mixture and cook until golden brown (about 3 minutes) stirring often.
Grease 4 small gratin dishes with the remaining oil and arrange the shrimp in a single layer over the bottom. Season shrimp with a bit of salt and pepper.
Sprinkle 1/2 cup of the breadcrumbs over the shrimp and top with tomato slices.
Cover with the remaining breadcrumbs and season with a bit more salt and pepper.
Melt the remaining 2 tsp of butter and drizzle over each gratin.
Bake at 450F until the shrimp are completely cooked (about 12 minutes).
Drizzle each gratin with 1 tsp vinegar before serving.