In a large Dutch oven, heat olive oil over medium heat. Add garlic; cook, stirring constantly, for 1 to 2 minutes or until lightly browned. Add spinach; cook, stirring constantly, for 3 to 4 minutes or until wilted. Cool spinach completely; drain spinach, and finely chop.
Preheat oven to 500°. Line a large rimmed baking sheet with aluminum foil.
In a medium bowl, combine panko, chopped spinach, goat cheese, Parmesan cheese, and green onion. Add butter, stirring to mix well. Place tomatoes, cut side up, on prepared baking sheet. Sprinkle tomato halves with salt and pepper. Divide panko mixture evenly among tomato halves. Broil 6 inches from heat for 6 to 8 minutes or until lightly browned.