Cook quinoa according to package suggestions - add 1/2 tsp lemon zest to water/broth during cooking.
In large skillet over medium/high heat, saute onion and carrot in 1 Tbsp olive oil 3-4 minutes, until onions are slightly softened. Add summer squash, saute 2-3 minutes, then add remaining lemon zest and frozen peas, saute until peas are warmed thru (about 5 minutes). Reduce heat to low, add cooked quinoa and chopped spinach to skillet, stir until quinoa and veggies are distributed evenly.
In a separate bowl, combine lemon juice and remaining olive oil (2 Tbsp) to create dressing, add to quinoa/veggie mixture. Salt and pepper to taste. Serve warm or cold.