Heat the oven to 400 degrees.
Place the olive oil, onion, zucchini, fennel and 1 teaspoon salt into a medium sized skillet and cook over medium heat until softened, about 8 minutes. minutes.
Cook the farro according to the instructions. Once cooked (and while still warm), add 2 cups of the farro into the skillet with the vegetables. Over low heat, stir in the gorgonzola and fennel leaves. Stir until the gorgonzola is completely melted.
Distribute about 1/4 teaspoon kosher salt evenly inside each tomato. Fill the tomatoes with the farro mixture and place the tomato tops back onto the tomatoes. Place into the oven and bake for 30-45 minutes, or until the tomatoes are softened and the inside is bubbly.
Remove from the oven and remove the tops. Place chopped fennel leaves on top of each tomato. Serve warm with gorgonzola and chopped fennel to taste.