Prepare your protein choice. For homemade seitan, slice into strips or cubes. For baked tofu, preheat your oven to 400°F (200°C) and bake for 25 minutes.

In a large skillet, heat 2 tablespoons of toasted sesame oil over medium heat. Add the finely chopped yellow onion and sauté for 5 minutes until translucent.

Add the chopped broccolini with a splash of water and cook for an additional 6-8 minutes until tender.

In a bowl, whisk together the soy sauce, rice vinegar, sesame oil, minced garlic, minced ginger, and agave syrup. In a separate bowl, mix cornstarch with a splash of sauce, then stir back into the mixture.

Add fresh Udon noodles to the skillet, cover, and cook for 2-3 minutes until heated through.

Pour the sauce over the noodles and veggies, add the protein, and cook for 3-4 minutes until the sauce thickens and coats the noodles.

Transfer to plates and garnish with chopped cilantro, sliced green onions, and sesame seeds before serving.