Pre-heat grill on medium/high for just a few minutes.
Put cherries, blueberries, and honey in a small cast iron skillet on the grill.
Put slices of pineapple and grapefruit cut side down on the grill.
Close lid and let cook for 5 minutes.
Check fruit for grill marks and flip. Give fruit in pan a stir.
Cover and let grill another 5-7 minutes.
Pull fruit off grill.
Run paring knife around inside edge of grapefruit, then gently turn peel partially inside out to release as much of grapefruit as possible. Scrape out remaining grapefruit and remove separators and pulp.
Mix together all fruit in pan then fill grapefruit shells and serve.