Wash and dry the spinach thoroughly, then slice the strawberries, cucumber, onion, and avocado into thin even pieces for balanced texture and easier serving.
Toast the walnuts or pecans in a dry skillet over medium heat for several minutes until fragrant and lightly golden to deepen their flavor and improve crunch.
Whisk together olive oil, balsamic vinegar, honey, Dijon mustard, garlic, salt, and pepper until the dressing becomes smooth and well combined.
Add spinach, strawberries, cucumber, onion, cranberries, nuts, and feta cheese into a large bowl, then place avocado slices on top carefully.
Drizzle the dressing over the salad just before serving and toss gently until the ingredients are lightly coated without crushing delicate toppings.