Chop the onion, garlic, peppers, and mushrooms into bite-sized pieces.
Heat a large skillet over medium-high heat. Sauté the onion and garlic for 2 minutes until fragrant. Add the peppers and mushrooms, and sauté for 5 minutes until softened and tender.
Season the frozen pollock fillets to taste with salt and pepper. In the same skillet or a separate pan over medium-high heat, cook the pollock for 4-5 minutes per side until the flesh is opaque and cooked through (internal temperature 63°C / 145°F).
Reduce heat to medium. Add the cream cheese and ajvar to the skillet with the vegetables and fish. Stir gently for 2-3 minutes until the cream cheese is fully melted and creates a smooth, creamy sauce.
Serve immediately on plates, dividing the fish, vegetables, and sauce evenly.