In a dry skillet over medium heat, add slivered almonds and toast for about 4 minutes, stirring frequently until they turn golden brown and fragrant.

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

Thoroughly rinse and dry the romaine lettuce and spinach to remove any grit; tear the romaine into bite-sized pieces and leave the spinach leaves whole.

In a large mixing bowl, combine the torn romaine and spinach. Gently toss them together, then top with crumbled feta cheese, thinly sliced red onion, and fresh strawberry slices.

Just before serving, drizzle the vinaigrette over the salad, or place it on the side for guests to add their preferred amount.