Preheat and Prepare for Roasting: Preheat your oven to 425°F (220°C) and arrange racks in the upper and lower thirds. Line two large baking sheets with parchment paper for easy cleanup.
Roast the Summer Vegetables: Evenly spread the eggplant, zucchini, and yellow squash across the two baking sheets. Drizzle each pan with 1 tablespoon olive oil, tossing to coat. Add a generous sprinkle of salt and a few grinds of black pepper. Roast for 25–30 minutes, swapping racks halfway through, until vegetables are tender and lightly caramelized at the edges. Let cool slightly.
Cook the Quinoa Fluffily: In a small saucepan, combine ½ cup rinsed quinoa with 1 cup water. Bring to a boil over medium-high heat. Once boiling, cover, reduce heat to low, and simmer for 15 minutes, or until all water is absorbed. Remove from heat and let it sit, covered, for 5 minutes. Fluff with a fork and let it cool slightly.
Toast the Almonds or Pine Nuts: Meanwhile, place the sliced almonds or pine nuts in a dry skillet over medium heat. Stir frequently for 4 to 8 minutes, until golden and fragrant. Remove from heat immediately and transfer to a small bowl to cool.
Build the Lemon-Garlic Dressing: In a large serving bowl, whisk together 2 tablespoons lemon juice and the minced garlic. While whisking, slowly stream in the remaining 2 tablespoons olive oil until emulsified.
Assemble the Salad: To the bowl with the dressing, add the roasted vegetables, cooked quinoa, halved tomatoes, chopped basil and mint, and the toasted nuts. Gently toss everything to combine. Season generously with salt, pepper, and more lemon juice to taste.
Add Creamy Finishing Touches: If using feta, fold in ½ to ¾ cup crumbled feta cheese just before serving. Serve at room temperature for best flavor, or chill if preparing ahead.