Heat 1 tablespoon of the oil in a large skillet over medium. Add poblano and onion; cook, stirring occasionally, until tender, about 8 minutes. Add garlic and cumin; cook, stirring often, until fragrant, about 1 minute. Transfer mixture to a food processor; add cilantro, salt, pepper and remaining 2 tablespoons oil.

While poblano and onion cook, place water in a large microwavable bowl, and microwave on HIGH until hot, about 4 minutes. Add spinach, and let stand 1 minute. Remove spinach, and squeeze between paper towels to remove excess moisture. Add spinach to mixture in food processor. Process until smooth, about 45 seconds, stopping to scrape sides as needed.

Cook rice according to package directions. Transfer to a large bowl, and stir in cilantro mixture. Top with queso fresco, and, if desired, additional chopped cilantro. Serve immediately.