Notes: To have quinoa and stew ready at the same time, start quinoa once you've added the potatoes to the stew (step 1). Small squid (calamari) are sold cleaned and cut into rings at many specialty stores and seafood markets.
1 tablespoon olive oil
1 onion (8 oz.), peeled, halved, and thinly slivered lengthwise
2 cloves garlic, peeled and minced
1 can (32 oz.) diced or crushed tomatoes
8 ounces red or white thin-skinned potatoes (about 1 in. wide), scrubbed and quartered
1 or 2 fresh hot green chilies such as jalapeños, rinsed, stemmed, seeded, and minced
1/2 teaspoon ground cumin
1/2 teaspoon chili powder
1/2 teaspoon salt
12 ounces shelled, deveined shrimp (31 to 40 per lb.), rinsed
8 ounces tilapia or other white-fleshed fish, rinsed and cut into 1-inch chunks
4 ounces fresh or thawed frozen calamari rings (optional; see notes), rinsed
Heat oil in a 5- to 6-quart pan over medium-high heat; add onion and garlic and stir often until onion is very limp, 8 to 10 minutes. Add tomatoes, 1 1/2 cups water, potatoes, chilies, cumin, chili powder, and salt; increase heat to high and bring to a boil. Reduce heat, cover, and simmer until potatoes are tender when pierced, 20 to 25 minutes.
Stir in seafood, if using. Cover and simmer until shrimp and fish are opaque but still moist-looking in the center of thickest part (cut to test), 3 to 4 minutes. Stir in cilantro. Spoon quinoa onto rimmed plates; top with stew.