Begin by heating a dry skillet over medium heat. Add the slivered almonds and toast them, stirring frequently for about 4 minutes, until they turn golden brown and release a nutty aroma. Once toasted, transfer them onto a plate to cool completely.

In a blender, combine olive oil, cider vinegar, mustard, minced garlic, shallot, one diced strawberry, honey, and a pinch of salt. Blend or shake vigorously for about 30 seconds until the mixture is emulsified and smooth.

Rinse the spinach and romaine lettuce under cold water, then dry them thoroughly using a salad spinner or paper towels. Tear or cut the romaine into bite-sized pieces.

In a large mixing bowl, combine the washed greens, crumbled feta, sliced red onion, and the remaining sliced strawberries. Gently toss these ingredients together.

Just before serving, drizzle the prepared vinaigrette over the salad, or keep it on the side if you prefer to serve it separately.