Start by preheating your oven to 350°F. Spread the slivered almonds evenly on a baking tray. Toast them in the oven for about 6 minutes, or until they are lightly golden and fragrant. Keep an eye on them—they can burn quickly! Once toasted, remove from the oven and set aside to cool.
While the almonds are cooling, place the fresh spinach into a large mixing bowl. Add the sliced strawberries, thinly sliced red onion, and crisp cucumber slices. Gently toss them together with clean hands or salad tongs to evenly distribute the ingredients and keep the delicate items like strawberries from getting bruised.
In a mason jar or any container with a tight lid, combine balsamic vinegar, olive oil, Dijon mustard, maple syrup, chopped garlic, and salt. Secure the lid and shake vigorously for about 15–20 seconds, or until the dressing looks emulsified and smooth. Taste and adjust seasoning if needed—more syrup if too tangy, or more mustard if too mild.
Pour about half of the vinaigrette over the salad and toss gently to coat everything evenly. You can always add more dressing later if needed. Just before serving, sprinkle the toasted almonds over the top for a satisfying crunch. Serve immediately to maintain the fresh texture of the spinach and strawberries.