Combine cucumber, green onions, cilantro, 4 1/2 tablespoons olive oil, 1 1/2 tablespoons white balsamic vinegar, and serrano chiles in a food processor.

Pulse the mixture until finely chopped.

Transfer the mixture to a bowl and season with more vinegar, salt, and black pepper to taste.

Sprinkle the mahi-mahi fillets on both sides with salt, pepper, and ground cumin.

Heat the remaining 1 tablespoon olive oil in a large nonstick skillet over medium-high heat.

Add the fish fillets to the skillet and cook for 5 minutes per side.

Turn the fish over, cover the skillet, and cook for an additional 4 to 5 minutes, or until the fish is just opaque in the center.

Divide the gazpacho sauce among 4 plates.

Top each serving of gazpacho sauce with one mahi-mahi fillet.

Scatter halved cherry tomatoes atop and around the fish.

Serve immediately.