Whisk together shallots, basil, lemon juice, paprika, cumin, oil, saffron, and garlic. Pour into a resealable plastic bag and add pork; zip shut and chill for 24 hours, flipping a few times.
Take pork out of bag, throwing away marinade. Season pork with salt and pepper. Lay pork on a cooking spray coated grill rack and cook 9 minutes per side or until a meat thermometer reads at least 155 degrees F. Let rest 10 minutes before slicing.
Meanwhile, arrange onion and bell peppers on a cooking spray coated grill rack and cook 4 minutes per side for onions and 12 per side for peppers. Put peppers in a resealable plastic bag and let sit 10 minutes. Take peppers out of bag, peel off skin, and slice in half lengthwise, throwing away seeds and membranes. Finely dice onions and peppers. Mix onions, peppers, basil, sugar, vinegar, and salt in a bowl and serve with pork.