Cook cumin seeds in a small skillet over medium-high heat 3 minutes or until seeds are lightly toasted; remove from heat, and let cool. Peel shrimp, and devein, if desired. Cut a slit almost through back of each shrimp. Place shrimp in a large heavy duty, zip-top plastic bag. Combine cumin seeds, chilies, yogurt, lemon juice, red pepper, salt, pepper, garam masala and garlic; pour over shrimp. Seal bag securely, and shake until shrimp are well coated. Marinate in refrigerator 4 hours, turning bag occasionally.