Rinse and roast the poblanos in the oven at 400°F for about 30 minutes.
Let the poblanos cool, then peel off any loose skin, and discard the stems and seeds.
Blend the roasted poblanos with 1/2 small onion, 1 peeled garlic clove, 10-15 sprigs of cilantro, and a handful of spinach (if using). Add a splash of stock if needed to blend smoothly.
Heat a splash of olive oil in a saucepan over medium heat. Add 1 cup of rice and cook, stirring regularly, until the rice is opaque and golden brown.
Stir in the blended mixture and cook for a couple of minutes. Add 1.5 cups of stock and 1/2 teaspoon of salt. Bring to a boil, then reduce heat to simmer, cover, and cook for 15-20 minutes until the liquid is absorbed.
Remove from heat and let it sit, covered, for a few minutes.
Taste and adjust the salt if needed, then serve. Store leftovers in an airtight container in the fridge.