Sauté the vegetables. Generously coat the bottom of a medium-sized pot with olive oil, and place it over medium-low heat. Add the onion and garlic and cook, stirring often, until soft, about 7 minutes. Add the Poblanos and cumin. Again, stirring often, cook until soft, about 4 minutes.
Blend some of the vegetables. Remove ¼ cup of this mixture from the pot, and add it to a blender along with 1 cup of the chicken stock. Blend until smooth, about 10 seconds. Set aside.
Sauté the rice and cook. Add the rice to the pot with the remaining onion-Poblano mixture, and stir to coat all of the grains — they should be shiny from the oil. If they're not, add a bit more oil. Sauté for a couple of minutes, and then pour in the blended poblano-onion-stock mixture, and the remaining stock. Turn the heat to high, and bring to a boil. Immediately reduce the heat to low, cover the pot, and gently simmer until all of the liquid has been absorbed and the rice is tender, about 20 minutes.
Add lemon juice and cliantro and season. Mix in the lemon juice and cilantro, and then season to taste with salt and pepper and serve. (Here's How to Season to Taste.)