In a blender or a small food processor, purée the avocado, water, mayonnaise and lemon juice until smooth. Season with salt and pepper. Set aside.
With the rack in the middle position, preheat the oven to 425°F (220°C).
On a non-stick baking sheet, or a baking sheet lined with a silicone mat, combine the potatoes with 2 tbsp (30 ml) of the oil. Season with salt and pepper.
Roast for 15 minutes or until tender and lightly browned. Let cool.
Meanwhile, in a pot of salted boiling water, cook the quinoa until tender, about 15 minutes. Drain and transfer to a bowl. Add the lemon zest and 1 tbsp (15 ml) of the oil. Season with salt and pepper. Set aside.
In a large non-stick skillet over medium-high heat, cook the salmon in 1 tbsp (15 ml) of the oil for 6 to 8 minutes, turning the fish over halfway through, or until the desired doneness. Season with salt and pepper. Set aside on a plate lined with paper towel.
In another bowl, combine the zucchini, lemon juice and remaining oil. Season with salt and pepper. Let marinate for 5 minutes.
Divide the potatoes, quinoa, salmon, zucchini, spinach and cherry tomatoes among four bowls. Garnish with the avocado sauce and spicy mayonnaise, to taste. Sprinkle with the pumpkin seeds.