You can make a double batch of roasted tomatoes early in the week (say, for this whole-wheat penne dinner) and save half for this recipe. With the tomatoes already prepared, the rest of the preparation will only take 15 minutes.
Preheat broiler. Toss tomatoes and onion with 2 teaspoons oil, 1/2 teaspoon salt, and the red-pepper flakes. Broil on a rimmed baking sheet until tomatoes are just starting to brown, 5 to 7 minutes.
Transfer tomatoes to a 9-inch square baking dish. Broil bread until golden, about 1 minute per side. Halve 1 garlic clove, and rub bread with a cut side. Thinly slice all garlic.
Rinse broccoli rabe, leaving slightly wet. Toss with 2 teaspoons oil, 1/4 teaspoon salt, the garlic, and lemon juice. Broil until leaves begin to brown, about 1 minute. Turn with tongs. Broil, turning once, until just tender, about 2 minutes.
Stir beans and oregano into tomatoes. Dot with ricotta. Drizzle with remaining 2 teaspoons oil. Broil until bubbling, 3 to 5 minutes. Serve over toast and with broccoli rabe on the side.