Preheat oven to 450°F (230°C).
Lay orzo out on a sheet pan without parchment paper. Toast in oven until golden brown, approximately 7 minutes, tossing half way through.
In a deep pan over medium heat, sweat the onions and garlic with 2 Tbsp (30 mL) oil. Add orzo and 2 cups (500 mL) stock. Continue to cook and add stock until orzo is 90% cooked to a dry consistency.
While orzo is cooking, sauté zucchini with 2 Tbsp (30 mL) oil on medium heat and set aside.
Season finished orzo with butter, remaining oil, and red pepper flakes. Add lentils and zucchini.
Just prior to serving, mix in arugula, dress with lemon juice, and season with salt and pepper.