In a large skillet combine caraway seeds, cumin seeds, and coriander seeds. Cook over medium-high heat for 2 to 3 minutes or until seeds are lightly toasted and fragrant, shaking the skillet constantly. Cool. Transfer seeds to a clean coffee grinder; pulse to form a fine powder.
For spice paste, in a small bowl stir together the spice seed powder, tomato sauce, chili paste, oil, chili powder, and garlic.
Trim fat from roast. Place meat in a shallow dish; sprinkle with salt and pepper. Spread spice paste over both sides of meat. Cover and marinate in the refrigerator for 2 hours.
For a charcoal grill, arrange medium-hot coals around a drip pan. Test for medium heat above pan. Place roast on grill rack over pan. Cover and grill to desired doneness, turning once halfway through grilling. Allow 35 to 40 minutes for medium rare (135 degrees F) and 40 to 45 minutes for medium (150 degrees F). (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Place roast in roasting pan; place pan on grill rack over the burner that is turned off. Grill as directed.)
Remove meat from grill. Cover meat with foil; let stand for 15 minutes. Temperature of meat will rise 10 degrees F during standing.