Place the sliced almonds in a dry skillet over medium heat. Stir constantly until they turn lightly brown, about 5 minutes. Transfer to a plate and let cool.
In a large bowl, add the baby spinach, strawberries, blueberries, and cucumber. Gently fold in the crumbled feta cheese and the cooled, toasted almonds.
In a small bowl, whisk together the olive oil, balsamic vinegar, honey, mustard, minced garlic, salt, and pepper.