Heat olive oil in a large skillet over medium-high heat. Add garlic and saute until light golden and fragrant, about 30 seconds.
Add in zucchini, squash and corn and season with salt and pepper to taste. Saute until just tender crisp, about 4 minutes (it will continue to cook slightly once removed from heat so don't overdo it).
Remove from heat and toss in tomatoes and let cool slightly (then strain off juice at the bottom if there is any).
Pour into a medium salad bowl and toss in lemon, parsley, basil and feta. Serve immediately.