Remove cauliflower rice from the freezer to thaw on the counter while you prepare the chicken and other components.
Trim the chicken breasts and cut each one lengthwise into 2–3 strips depending on size; place the strips in the Instant Pot insert.
Grate the zest from 2 lemons, then halve and juice them.
In a bowl whisk together lemon zest and juice, 1 tablespoon Greek seasoning, 2 tablespoons olive oil, 1/4 cup chicken stock, 1/2 tsp Greek oregano, and 1/2 tsp fresh-ground black pepper to make the cooking sauce.
Pour the sauce over the chicken in the Instant Pot, close the lid, set to Manual/High Pressure for 8 minutes, then allow a natural release for 10 minutes before releasing any remaining pressure.
When pressure is fully released, use a slotted spoon to remove the chicken to a cutting board, leaving the cooking liquid in the pot; if there is excessive liquid, use the Sauté function on high for a few minutes to reduce it.
Shred the chicken with two forks, return it to the Instant Pot, and stir gently so the shredded chicken is coated with the sauce; keep warm on the Low setting while finishing the rice and salsa.
Make the Greek salsa by chopping cucumbers, tomatoes, Kalamata or black olives, and red onion; toss them in a bowl with 1/4 cup Italian dressing and gently stir in crumbled feta.
Chop the yellow onion and green pepper for the cauliflower rice.
If using fresh cauliflower, remove leaves and chop into small pieces and pulse in a food processor or grate to make 'rice.' If using frozen, use semi-thawed cauliflower rice.
Heat 1 tablespoon olive oil in a large nonstick skillet over medium-high heat, add the chopped green pepper and yellow onion, and cook about 3 minutes until softened and beginning to brown.
Add 1 tablespoon Greek seasoning to the skillet and cook 1 minute, then add the cauliflower rice and cook, stirring occasionally, until heated through and some moisture has evaporated, about 3–4 minutes for frozen or slightly longer for fresh; season with salt and fresh-ground black pepper to taste.
To assemble bowls, place cauliflower rice in the bottom of each bowl, add a generous scoop of shredded lemon chicken, and top with a scoop of Greek salsa; serve immediately.