Preheat the oven to 350°. Fit a large baking pan with a metal cooling rack and arrange the bacon slices on one layer; bake until crispy, about 15–17 minutes. Cool the bacon and transfer it to a cutting board; chop it roughly and set aside.
Place the peas in a medium pot, add enough water to cover the peas by 1 inch, and set over medium-high heat. As the water simmers, skim off the foam that rises to the top; when the water comes to a boil, cover, reduce the heat to low, and simmer the peas until tender, about 40–45 minutes.
Meanwhile, fill a bowl with iced water. When the peas have finished cooking, drain and immerse them into the ice bath; let them cool for 15 minutes and then drain.
In a large bowl, combine the peas, corn, tomatoes, onions, garlic, vinegar, oil, salt, and pepper. Cover and chill for 30 minutes. Before serving, stir in the bacon and serve immediately.