Slice squid bodies into 1/2-inch-thick rings; leave tentacles whole. Rinse carefully inside and out and pat dry. Set aside. Scrub lemon and cut crosswise into 1/8-inch-thick slices. Cut each slice into quarters and set aside.
Heat 1 1/2 teaspoons oil in a large heavy skillet over high heat. Add half of the peppers and 1/4 teaspoon crushed red pepper; sauté until barely tender, 1 to 2 minutes. Add half of the squid and sauté until opaque, 30 to 45 seconds. Add half of the lemon pieces and sauté until the lemon is just heated through, 30 seconds longer. Transfer the squid mixture to a serving dish and keep warm.
Add the remaining 1 1/2 teaspoons oil to the pan and heat over high heat. Cook the remaining peppers, crushed red pepper, squid and lemon in the same manner.
Transfer to the serving dish. Season with salt and pepper. Sprinkle with cilantro and serve immediately.
Note: Calamari, also known as squid, is sold frozen or fresh in the seafood department of the grocery store. Look for cleaned calamari, with its cartilage and ink removed; otherwise ask at the fish counter to have it cleaned.