Toast the almonds: Add the almonds to a large skillet and heat over medium. Cook, stirring constantly to prevent burning, for 2 minutes. Reduce the heat to medium-low. Continue cooking and stirring until they are fragrant and just starting to turn golden, about 3 to 5 minutes more. Immediately transfer to a plate or bowl to cool.
Place the sliced onion in a bowl and cover with cold water. Let sit while you prepare the rest of the salad (this keeps the flavor but removes the harsh onion bite).
Make the dressing: In a medium bowl or liquid measuring cup with a spout, briskly whisk together the lemon juice, oil, honey, mustard, salt, and pepper until evenly combined.
In a large bowl, place the romaine and spinach. Add the strawberries, tomatoes, and 1 of the avocados. Sprinkle with salt. Drain the red onion, pat it dry, and add it as well. Add the chicken. Spoon about half of the dressing over the salad and toss to coat (I find that clean hands are an ideal tool for tossing). Assess the amount of dressing. You want the leaves to be nicely moistened but not swimming in dressing. Add a little more if needed to suit your preferences.
Add the remaining avocado, feta, and almonds. Toss again lightly to combine. Serve immediately, with extra dressing on the side as desired.