Heat 2 tablespoons of the oil in a large heavy skillet over medium heat. Add the garlic, jalapeno, cumin and oregano; cook for 30 seconds or until fragrant. Stir in the corn. Increase the heat to medium-high; cook for 2 minutes. Add the 1/2 cup water; cover and cook for 2 minutes. Scrape into a large bowl. Stir in the salt. Cool to room temperature.
Bring a medium-size saucepan of lightly salted water to boiling. Add the peas; cook for 3 to 5 minutes for fresh, or 2 minutes for the frozen. Drain the peas in a colander; rinse under cold water. Add the peas, black beans, tomato, green onion and cilantro to the corn mixture in the bowl.
Whisk together mustard, pepper and lime juice in a small bowl. Gradually whisk in the remaining olive oil. Pour over salad; toss well to coat. Cover and chill for at least 1 hour. Serve cold.