Combine 2 tbsp garlic, 2 tbsp olive oil, 1/2 tsp salt, 1/4 tsp pepper and all of the oregano to a small bowl.
Coat the fish in this mixture, cover and chill for 1 hour.
Meanwhile, soak the olives in cold water for 30 minutes then drain and chop.
Combine 4 tbsp olive oil and the chives in a food processor until a sauce-like mixture forms.
Heat 2 tbsp olive oil in a skillet over medium-high heat. Sauté the shallots until soft (about 2 minutes).
Add the garlic, thyme and olive and cook until heated through (about 3 minutes).
Add the remaining salt and pepper to the olives, remove from heat, cover and keep warm.
Remove the mahi mahi from the refridgerator and grill until cooked through and fish flakes easily with a fork (about 4 minutes per side).
Spoon the olive mixture over the top of each piece of fish and drizzle with the chive mixture before serving.