Drizzle canola oil to coat two 8-inch cazuelas or oven-safe dishes. Arrange the potato slices in one even layer on the bottom. Season with salt and pepper and drizzle with more canola oil on top. Bake until the potatoes just begin to brown around the edges and the centers are slightly soft when poked with a fork, 12 to 15 minutes.
Meanwhile, whisk together the mustard and lemon juice in a medium bowl; season with salt and pepper. Continue whisking while drizzling in the olive oil until the sauce is emulsified. Add the parsley and mix to combine.
Once the potatoes are cooked through, place one salmon fillet in each of the baking dishes and drizzle with canola oil; sprinkle with salt and pepper. Reduce the oven temperature to 250 degrees F and bake to medium doneness, about 15 minutes.
Spoon the sauce over the top of the salmon and garnish with the thyme, parsley and lemon zest to taste.