How to Make It
Heat oil in a medium saucepan on side burners or grates of the grill. Add onion and garlic and cook until soft. Add red pepper flakes and cook for 1 minute. Add remaining BBQ sauce ingredients, season with salt and pepper and cook until sauce has thickened, 25 to 30 minutes.
Whisk together vinegar, garlic, 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.
Season steaks on both sides with salt and pepper. Grill over high heat until golden brown, 4 to 5 minutes. Turn and continue grilling for 4 to 5 minutes for medium-rare meat; baste with the BBQ sauce during the last few minutes. Remove from the grill and brush with more of the BBQ sauce. Let steaks rest for 5 minutes, then slice 1/4 inch thick. Spoon the cherry pepper-tomato relish over the steak and garnish with parsley leaves.