Heat Olive Oil in a heavy bottom skillet and add onions. Saute until golden and add minced garlic. Stir for a minute or two.
Add rice and salt and stir until rice is golden. Add sherry and stir until liquid is absorbed. Then add the hot chicken broth, stir and bring to a boil. Cover and turn the heat to simmer and cook for about 10 or 15 minutes.
Add the peas, raw shrimp or cooked chicken at this point and cook for another 5 - 10 minutes (check to see if liquid is absorbed and shrimp are opaque.) If liquid isn't absorbed, continue cooking for another few minutes, but watch it - you don't want it dry, just moist. Check for seasonings and add more salt and pepper if needed.
Note: If using raw chicken, cube chicken and saute in a little Olive Oil until golden, but don't overcook. Add chicken when you add the peas, before all liquid is absorbed.