Garlic: Sauté minced garlic until fragrant, then cook with the quinoa to infuse it with extra flavor. 1-2 cloves or adjust to taste.
Avocado: Add diced avocado to the Southwest quinoa salad just before serving (as it will brown while sitting).
Spice: Add a pinch of red pepper flakes or some finely chopped chili.
Pickled ingredients: Pickled red onion or pickled jalapenos, finely chopped, are a great addition to this Mexican quinoa recipe in place of their fresh counterparts.
Tofu: Marinated or lightly fried tofu with taco seasoning (or something similar with a bit of heat) could work very well. Here’s a great guide to tofu if you want to learn more about this protein-packed food!
Other vegetables: corn (frozen, canned, or charred), spinach or kale, crispy chickpeas, black olives, cucumber (English or Persian), roasted sweet potato, etc.
Nuts/Seeds: Add extra crunch and nutrients with pepitas, sunflower seeds, hemp seeds, cashews, etc.