Add rice, chicken broth, and butter into a pot. Bring to a boil on high, stir once and cover. Simmer on low for 20 minutes, then remove from heat and keep covered for 5 to 10 minutes longer.
Meanwhile, in a skillet, on medium-low heat cook the onions in oil for 6 minutes or until just about to brown. Add garlic to pan and cook for 30 more seconds. Stir in the tomato paste and cumin and cook for 1 minute. Mix in cooked rice, lime juice, and cilantro, and add salt to taste.