Wash and dry the spinach thoroughly.
Rinse the strawberries, hull them, slice them, and gently pat them dry.
Toast the nuts in a dry skillet for 2 to 4 minutes, shaking often, then let them cool.
Make the dressing by stirring the balsamic vinegar and honey together, then whisking while slowly pouring in the olive oil; season with salt and pepper and adjust to taste.
Assemble the salad in a large bowl with spinach first, then strawberries, nuts, cheese, and any optional onion, avocado, or protein.
Dress right before serving, toss gently, and taste again before serving.