Pre-heat oven to 425 degrees.
Place the peppers cut-side down on a baking sheet with a lip or a baking pan. Bake for 10 minutes. Turn peppers over and bake for an additional 5 minutes. Repeat previous step two more times. Total baking time is 25 minutes.
Remove tray from oven and cover with a clean dishtowel for 10 minutes. The peppers should be soft and tender and you can easily slip off the skins.
Cut the green peppers into a 1/4 inch dice. Slice the red pepper halves in half (now they will be quarters) and reserve.
Add 1 tablespoon of oil to a non-stick skillet over medium heat. Add onions and stir for a minute, then add garlic and stir for 30 seconds. Add the green peppers, lower the heat a bit and cook for 5 minutes. Add tomatoes, cumin and cayenne and mix well. Cook an additional 6 minutes looking for the mixture to loose some of its moisture.
Combine the ingredients for the dressing in a small bowl and whisk.
To assemble your salad, arrange the red pepper quarters on a serving platter -- a la spokes on a wheel or flower petals. Its fine if the overlap a bit. Drizzle dressing over the red peppers. Spoon the green pepper-tomato mixture into the center -- allowing some to casually spill over.
Alternately, you can arrange this on single serving platters with 2 red pepper quarters in a V-shape and the green pepper-tomato mixture placed where the two strips join together.
This salad can be served chilled or at room temperature.