In a small jar with a lid, combine the olive oil, apple cider vinegar, Dijon mustard, garlic, maple syrup, salt, and pepper.
Close the lid tightly and shake the jar until the ingredients emulsify into a smooth, velvety dressing.
Place the spinach leaves in a large bowl. Add the dressing and toss to coat the leaves.
Arrange the coated spinach leaves on a serving platter. Scatter the red onions on top.
Add the pecan halves and goat cheese crumbles, evenly spreading them on the spinach leaves.
Serve immediately.
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Notes
The pretty presentation is a big part of this salad's appeal. That's why I coat the spinach in the dressing and arrange the other ingredients on top instead of just mixing everything in a bowl.
Pecans are delicious raw, but you can spread them on a rimmed, parchment-lined baking sheet and toast them in a 300°F oven for 15 minutes if you wish.
Acceptable substitutions include walnuts instead of pecans and crumbled feta instead of goat cheese (but goat cheese is creamier and pecans are sweeter).