Bring 3 cups of water to a boil in a pot over high heat. Add the green beans and cook for just 2-3 minutes until they turn bright green and are tender-crisp—you want them to maintain their bite and vibrant color. Immediately transfer the beans to a bowl of ice water to stop the cooking process, then drain and set aside. This blanching technique locks in the color and ensures perfect texture.
While the beans cook, cut the bacon into bite-sized pieces and cook in a large skillet over medium-high heat, stirring occasionally, until crispy and golden (about 8-10 minutes). Transfer the cooked bacon to a paper towel-lined plate. Reserve 1.5 tablespoons of the bacon fat in a small bowl—this is liquid gold for your dressing. In the same skillet (no need to clean it), toast the pecans over medium heat for 2-3 minutes, stirring frequently, until fragrant and lightly browned. Transfer to a plate.
Add the olive oil to the same bacon-flavored skillet and warm over medium heat. Add the thinly sliced red onion and cook for 3-4 minutes, stirring occasionally, until softened and slightly caramelized. The onion should still have a bit of crunch but become sweeter and milder. I like to add a small pinch of salt here to help them release their juices and soften faster.
In the small bowl with the reserved bacon fat, whisk together the red wine vinegar, Dijon mustard, honey, and a pinch of salt and black pepper. Whisk until the honey dissolves and the dressing emulsifies slightly. Taste and adjust seasonings as needed—the dressing should be tangy with a subtle sweetness and savory richness from the bacon fat. Don't be shy with the pepper; it adds a welcome bite to balance the richness.
In a large serving bowl, combine the blanched green beans from Step 1, the softened onions from Step 3, the crispy bacon from Step 2, and the toasted pecans from Step 2. Pour the dressing from Step 4 over everything and toss gently but thoroughly, ensuring every bean is coated with the vinaigrette. Serve immediately while the beans are still cool and the bacon is still crispy. The warm onions will slightly soften the cold beans while maintaining their texture.