In a large saucepan, braiser, or lidded skillet, saute onion and garlic over medium high heat, in olive oil until fragrant and tender, 4-5 minutes. Add the rice, saute 1-2 more minutes, coating each grain, then add coriander, cumin, salt, and half the lime zest, toast 1 minute.
Add the water (make sure to see notes on quantity). Bring to a rapid boil. Cover, then lower the heat to medium-low so it simmers gently. Cook 13-14 minutes, until the rice is tender and all the water is absorbed. Replace lid, let stand with heat off for 5 minutes.
Fluff with fork, squeeze with lime juice (2-4 tablespoons) and right before serving, toss in the chopped cilantro and scallions. Fluff again, taste and adjust salt and lime to taste.
