Combine olive oil, Dijon mustard, lemon juice, and honey in a mason jar. Whisk well with a fork for a minute or 2 until emulsified. Add more honey or mustard, to taste.
Assembly
Combine spinach, sliced peaches, blueberries, and crumbled feta cheese in a large serving bowl (or in 4 individual salad bowls).
Add salad dressing and toss to combine. Top with toasted pine nuts.
Notes
This salad works wonderfully as a side, appetizer, light lunch, or dinner when paired with your favorite protein.