Preheat the oven to 350. Heat 1 Tbsp. oil over medium heat in large skillet. Add the onion and leek and cook, stirring, until tender, about 3 - 5 minutes. Add the garlic, stir together until fragrant, about 30 seconds, and add the zucchini. Cook, stirring until tender, about 8 minutes. Season to taste with salt and pepper. Stir in the dill and mint. Remove from heat.