Add the onion, 2 tablespoons olive oil, the lemon juice, 1 teaspoon salt, and the sugar to a small bowl. Toss to combine, then let sit at room temperature for 30 minutes, until the onion softens.
2. Step
Meanwhile, bring a large pot of salted water to a boil. Add the corn, cover, and cook for 5 minutes, until tender. Remove the corn from the pot and let cool to the touch.
3. Step
Place corn on a cutting board with a damp paper towel and cut off the kernels. (The paper towel helps keep the corn from flying everywhere).
4. Step
Add the corn kernels to a large bowl with the tomato, avocado, and the pickled onions, along with the pickling liquid. Season with salt and pepper and toss to combine.
5. Step
Transfer to a serving bowl, then drizzle with olive oil and season with more salt and pepper.
