Preheat an outdoor grill or indoor grill pan to medium-high heat.
Cut the squash and zucchini vertically into 1/4-inch thick planks. Cut bell pepper into 3 or 4 big pieces. Toss in the salad bowl you’re going to use with 1 tablespoon olive oil, 1/2 teaspoon kosher salt, and a pinch of black pepper.
Grill vegetables until charred and tender, 3 to 5 minutes per side. The peppers will take longer than the squash and zucchini. Transfer to a cutting board and chop into 1-inch pieces.
Add 3 big handfuls of spinach to your salad bowl and use a fork and chef’s knife to chop the spinach into small pieces. Season with a pinch of salt and pepper.
Add the grilled vegetables, 1 sliced medium tomato, 1 thinly sliced Persian cucumber, 1/4 thinly sliced medium red onion, and 1/4 cup kalamata olives. Before you toss them into the spinach, season them well with a big pinch of salt and pepper.
Toss the salad together with desired amount of dressing. Taste and season with salt as desired.
Top with 1 cubed avocado and 4 ounces feta cheese. If you have them, garnish with a couple tablespoons of fresh oregano and mint leaves.