Place potatoes in a medium pot and cover with cold water. Bring to a boil then reduce heat to a simmer, about 10 minutes or until tender. Drain then place in a medium-size mixing bowl.

While the potatoes are cooking, add oil to a large skillet over medium-high heat.

Add the bacon and cook until crisp, 3–4 minutes per side.

Remove the bacon from the pan and add the onion, garlic, some salt, and pepper to the bacon drippings.

Cook until the onions are tender, about 5 minutes.

Remove pan from the heat and add mustard and vinegar, whisking vigorously to incorporate the dressing.

Pour the dressing over the potatoes and add the spinach, tossing to coat the potatoes and lightly wilt the spinach. Crumble the bacon over everything.

Serve warm or at room temperature.