Wash and dry spinach leaves thoroughly using a salad spinner. Pat with paper towels if needed to remove excess moisture.
Place the spinach in a large serving bowl.
Add sliced strawberries, crumbled feta cheese, toasted almond slices, and thinly sliced red onion to the bowl.
If using any optional ingredients, add them to the bowl.
Drizzle the balsamic vinaigrette over the salad.
Gently toss all ingredients to coat evenly with the dressing.
Taste and adjust seasoning if needed with a pinch of salt and freshly ground black pepper.
Serve immediately for the best flavor and texture.