Start by rinsing the quinoa under cold water using a fine mesh strainer until the water runs clear. This step removes the natural coating that can make quinoa taste bitter. Add the rinsed quinoa and broth to a saucepan, bring it to a boil, then cover and simmer on low for about 15 minutes, or until the liquid is absorbed.
While the quinoa cooks, pat the shrimp dry and toss it with half the chili powder, half the salt, and the cayenne pepper. Heat 1 tablespoon of olive oil in a skillet over medium-high heat and add the shrimp in a single layer. Sear for about two minutes per side until pink and just cooked through, then remove immediately so it doesn't turn rubbery.
In the same skillet, lower the heat slightly and add the remaining olive oil along with the minced garlic. Cook for about 30 seconds, stirring constantly, until it turns fragrant and just barely golden. Watch it closely here, because garlic can go from perfectly toasted to burnt in a matter of seconds.
Fluff the cooked quinoa with a fork and transfer it to a large mixing bowl. Pour the sautéed garlic and any oil left in the pan directly over the warm quinoa so it soaks up all that flavor. Add the chopped red onion and cherry tomatoes, then toss everything together gently.
Zest and juice the lemon directly into the bowl, then add the remaining salt and a good crack of black pepper. Toss in the fresh parsley or cilantro along with the seared shrimp, mixing just until combined. Taste and adjust the lemon or salt depending on how bright you want it.
Fold in the diced avocado so it stays intact and creamy rather than mushy. You can serve the salad warm right away, or let it chill in the refrigerator for 20 to 30 minutes if you prefer it cold. Either way, give it one more gentle toss before plating.