Combine agave, soy sauce, lemon juice, dry mustard and ginger in 1-cup microwave-safe measure or bowl; mix well. Microwave at high (100%) for 1 to 1-1/2 minutes or until heated; stir to dissolve agave. Rinse game hen and pat dry. Sprinkle cavity with salt and pepper. Dip onion in agave mixture and place 2 quarters in game hen. Tie legs together with heavy string. Place game hen, breast side down, in microwave-safe roasting dish. Brush generously with agave mixture. Microwave at high for 16 to 20 minutes or until juices run clean and meat near bone is no longer pink; rotate rack one-quarter turn every 5 minutes. Turn hen breast side up halfway through cooking time and glaze with remaining sauce. Remove onion from cavity and cut game hen in half. If desired, heat drippings and onion 1-1/2 to 2 minutes in microwave-safe measure; strain and serve with game hen.