Pour the water into the insert set in a 6- or 8-quart Instant Pot. If your stack set doesn’t come with a bottom layer that has feet to lift it up, you’ll also need to put a pressure-safe rack or trivet in the insert.
In the bottom layer of the stack set, spread the cauliflower rice. Set this in the insert (and on the rack, if necessary).
Gently toss the salmon cubes, harissa, and 1 tbsp olive oil in a medium bowl until the fish is well coated. Pour and scrape all of this mixture into the top layer of the stack. Do not cover. Set the top layer on the bottom layer in the insert. Lock the lid onto the pot.
For all models, set pot for Pressure Cook or Manual. Set level to High, valve must be closed. Set time for 6 Minutes with the Keep Warm setting off. If needed, press Start.
When the pot has finished cooking, use the quick-release method to bring the pressure back to normal. Unlatch the lid and open the cooker. Use hot pads or silicone baking mitts to transfer the (hot!) stacked layers to a nearby wire rack. Return the layer with the salmon to the pot and set the lid askew over the pot to keep the fish warm.
Spread the riced cauliflower into four serving bowls before you make the zhug (parsley sauce). To do so, put the parsley, cilantro, jalapeño, garlic, lemon juice, salt, coriander, and cumin in a food processor. Cover and pulse, adding the ⅓ cup olive oil through the feed tube to create a pesto-like sauce (if a tad thinner than standard pesto). You may need to add a little more olive oil, depending on the moisture content of the fresh herbs.
To serve, top each bowl of cauliflower rice with a quarter of the salmon cubes (leaving any liquid behind in the stacking container). Line the cucumber slices around about a quarter of each bowl. Top each serving with some zhug and tzatziki, as well as some cubed feta and minced dill for garnishes.
For a 3-quart Instant Pot, you must use 1 cup of water in the insert. You must then halve the remaining ingredients and you must use stacking containers that can fit in the smaller insert.
For a 5-quart Instant Pot, you can complete the recipe as stated but you must use 7-inch stackable containers specifically made to fit this slightly smaller pot. (Some standard stacking containers are too tall to work in these models.)
For a 10-quart Instant Pot, you must use 2½ cups of water in the insert. You can otherwise complete the recipe as stated.