Preheat the oven to 350ºF and line two baking sheets with aluminum foil, or spray with nonstick cooking spray.
A food processor works best for processing the cauliflower, a blender or grater will work as well, or purchase Relay Food's pre-grated cauliflower rice to save time. Add the florets to a food processor and pulse a few times, until the mixture resembles rice grains.
Add the cauliflower rice to a prepared baking sheet. Add oil and salt, toss well to combine, evenly spread out over the baking sheet, and add to the middle rack in the oven to bake for 18-20 minutes.
Rinse salmon fillets in cold water, and pat dry with paper towels. Fold aluminum foil into a bowl shape. Place aluminum bowl on top of a foil covered baking sheet. Lay a salmon fillet in each foil bowl and leave unsealed.
Pour milk over each fillet (pro tip: cooking fish in milk is a technique that helps create a tender and flaky fish and rids the fillet of unwanted “fishiness”). Drizzle half of the honey mustard sauce over each fillet. Season each fillet with pepper.
Bake for 20 minutes, depending on the thickness of the fillet, then broil on high for 5 minutes, until the sauce begins to bubble and slightly darken. The salmon should no longer be shiny, but rather an opaque pink shade that is firm and easily flakes with a fork.
Distribute an even amount of watercress and baked cauliflower rice on each plate. Sprinkle capers and slivered almonds over salmon fillets before plating.