Make the dressing: Whisk the lemon juice, garlic, cumin, chili, and salt in a serving bowl. Drizzle in the oil while whisking to emulsify.
Cook the couscous: Bring 2 quarts water to a boil in a saucepan with 1 tablespoon salt. Cook the couscous (or chosen grain) until tender or according to package directions. Drain and cool for 10 minutes.
Add the tomatoes, red and green onions, chili, cucumber and couscous to the bowl and toss gently to mix. Sprinkle the herbs and feta over the salad. Serve and enjoy.
Make ahead tip:
You can cook the couscous a few days ahead. Keep it in a container in the refrigerator, but assemble the rest of the salad when you're ready to serve.