In a large salad bowl, toss together the greens, radishes, onion, eggs, and tomatoes.
In a large skillet, cook the bacon over medium heat until crisp, about 7 minutes. Leaving the rendered bacon fat in the skillet, remove the bacon to drain on paper towels and crumble when cool enough to handle.
Heat the bacon fat in the skillet over medium-high heat. Stir in the vinegar, sugar, salt, and pepper. Swirl the pan over the heat for 1 to 2 minutes to concentrate the flavors and slightly thicken the dressing. Pour the hot dressing over the greens and toss quickly to coat. Sprinkle the greens with the crumbled bacon and blue cheese (if using).