Preheat your oven to 425 degrees. Grease a large baking sheet with non-stick cooking spray.
Toss the green beans and the potatoes 2 tablespoons of the olive oil & season them with salt & pepper. Spread the vegetables out in a single layer on the baking sheet. Roast the vegetables for 20-30 minutes, stirring every 10 minutes, until the potatoes are soft & the vegetables are just starting to brown.
While the vegetables are roasting, in a large skillet, fry the bacon over medium heat until crisp. Transfer to a paper-towel lined plate.
Discard all but 2 tablespoons of the bacon grease from the skillet and return to medium heat. Add the onions and cook, stirring, for about 2 minutes. Add the almonds to the skillet with the onions and continue cooking until the onions are soft & translucent. Stir in the vinegar, mustard and remaining tablespoon of oil to the skillet. Stir until just combined and heated through.
Pour the contents of the skillet into a large bowl. Crumble the bacon into the dressing. Add the roasted vegetables to the bowl and toss with the dressing. Transfer to a serving platter and sprinkle additional almond slices on top.