Toast pecans in a dry skillet over medium heat for 3-5 minutes until fragrant and lightly browned, then set aside to cool.

In a medium glass jar or whisking bowl, combine extra-virgin olive oil, apple cider vinegar, sugar, poppy seeds, dry mustard, and salt.

Whisk the dressing vigorously or shake the sealed jar until the sugar is fully dissolved and the emulsion is stable.

Place the prepared baby spinach in a large chilled mixing bowl.

Add the sliced strawberries and thinly sliced red onions to the spinach.

Drizzle approximately half of the dressing over the greens and toss gently with salad tongs until leaves are evenly coated.

Incorporate the cooled toasted pecans and crumbled feta cheese.

Transfer to individual serving plates or a large platter and serve immediately, providing remaining dressing on the side.