Process cilantro and spinach leaves in a blender with 2 tablespoons water. Reserve.
Heat the oil in a saucepan over high heat, add the onion, garlic, and aji Amarillo, stirring for 5 minutes over medium heat. Add the cilantro and spinach mixture, and fry for 5 minutes.
Add rice and vegetables, stir and add beer and vegetable stock. Bring to a boil.
Turn the heat to low, put the lid on, and cook for 20 minutes, undisturbed. Stir with a kitchen fork, and turn off the heat.
Serve with Salsa Criolla, if desired.