Heat olive oil in a pan. Add chopped onion and thyme. Add Arborio rice. Mix well with the onion. Pour some chicken stock. When the rice is cooked, add green peas. Pour some more chicken stock again. Season with salt. Turn off the gas when the peas are cooked. Add butter and grated parmesan cheese. Mix well. Transfer risotto to a serving plate. Garnish with some parmesan shavings and thyme.