Heat oil in a cast-iron skillet over medium-high heat. Add onion and jalapeño (if using), and sauté 3 minutes or until onion is tender. Add garlic, and sauté 30 seconds longer.
Add tomatoes, and cook 3 minutes or until tomatoes begin to break down.
Add okra, and cover. Cook 6 to 8 minutes, stirring occasionally, or until okra is crisp-tender. Season with salt and pepper.