Lobster cakes: In a large, deep-sided saucepan, heat the butter over a low heat until it stops foming. Add the flour gradually and cook for 2 minutes, whisking continually. Add milk 1/2 cup at a time, whisking constantly to get rid of the lumps. Simmer for 5 minutes, continuing to whisk until thick and smooth. Remove from heat and set aside.
In a large bowl, combine the lobster, peppers, scallions, cayenne, salt, and pepper. Add 1 cup of the bread crumbs and the milk mixture, and mix well. Cool to room temperature. Shape into 1-to 11/2 inch thick and flatten slightly. The lobster cakes should be about 1/2 inch thick. Coat the cakes with more bread crumbs.
Heat a layer of buter and oil in a saute pan over a medium heat until hot, not smoking. Cook the lobster cakes untill golden brown on both sides. Drain on paper towels and serve hot with tartar sauce.
Tomato Tartar Sauce: In a small bowl, whisk together the mayonnaise, lemon juice, and tomato paste. Add the onions, pickles, capers, and salt and pepper, and whisk until blended.