Heat oil in a large saucepan over medium-high heat. Add onions and cook until soft, about 4 to 5 minutes. Add garlic and red pepper flakes and cook for 1 minute. Add remaining ingredients, reduce heat to medium-low and cook until thickened, about 35 to 40 minutes.
Heat grill to high. Season steaks on both sides with salt and pepper. Grill, on 1 side, until crusty and slightly charred, about 4 to 5 minutes. Turn steaks over, close the hood and continue grilling for 6 to 8 minutes for medium-rare doneness. Baste with the sauce during the last few minutes. Remove from the grill and brush with more of the sauce. Let meat rest for 5 minutes, then slice into 1/4 inch thick slices and top with the Cherry Pepper-Tomato salad.
Whisk together vinegar, garlic and salt and pepper in a medium bowl. Slowly whisk in the olive oil. Add the peppers, tomatoes and parsley and stir to combine. Adjust seasoning and let sit 30 minutes at room temperature before serving.