Preheat grill or oven to medium-high heat (400°F – 450°F).
In a large cast iron skillet, warm oil until sizzling hot then add tomatoes, onion, garlic, and rosemary, and season with salt and pepper. Cook on medium-high heat with lid closed until tomatoes are blistered, garlic is fork tender and the backyard smells good enough to eat, about 15 minutes!
Open grill and work from grill or move skillet to stovetop. First, remove large pieces of rosemary. Next, add tomato paste to skillet, stirring continually until heated through, about 3 minutes. Then, add orange juice and zest to deglaze the pan, lifting the caramelized tomato bits from the bottom. Add remaining ingredients to pan, stirring to thoroughly incorporate. Allow to cook until mixture is thick and bubbly.
Remove from heat, puree with a stick blender or carefully pour into a blender and blend until smooth. Taste, and adjust seasonings as desire.
Pour over meat and vegetables for a marinade before BBQ-ing or grilling, or serve as a sauce to your favorite grilled dishes.
