SEASON CHICKEN: Sprinkle salt and pepper inside chicken cavity and add a couple chunks onion and lemon if desired. Combine all seasoning ingredients and smear 2/3 of it on chicken, including under the breast skin (gently loosen skin from flesh, then smear).
PREPARE FOR INSTANT POT COOKING: Put broth, onions and garlic clove into a 6-8 quart instant pot. Place trivet (that comes with pot) over the mixture. Place chicken on top, breast side up.
INSTANT POT SETTINGS/COOKING: Place on instant pot lid and turn clockwise to lock. Turn valve to SEALING. Push PRESSURE or MANUAL button. Use + or - buttons to set time. Calculate time at 6 minutes per pound LESS 1 minute. So a 3.5 lb chicken will take (3.5 x 6) - 1 = 20 minutes. Pressure will take 10-15 minutes to build before the pressure clock starts. When finished (instant pot will beep), wait 15 minutes for a NATURAL RELEASE, then do a quick release if necessary for the pressure button to pop down.
HEAT OVEN to 500F while chicken is cooking in instant pot. Prepare a pan, lined with foil and sprayed with oil. If desired, add veggies for roasting on half the pan, tossing them with olive oil, salt and pepper.
FINISH CHICKEN IN OVEN (WITH VEGGIES): Remove chicken from instant pot (I use two forks at either end - don't pierce meat). Place on prepared pan along side veggies if using. Brush on remaining seasoning. Roast for 10 minutes until skin browns. Instant thermometer should read 165F. Cut up chicken and serve with gravy.
MAKE GRAVY: While chicken is roasting in oven, discard onions and garlic from instant pot. Pour broth into a separator (or skim grease from broth and reserve). Put 2 tablespoons grease in saucepan. Heat to medium. Add flour and stir for 2 minutes. Add 2 cups broth. Continue cooking for a few minutes until thickened. Taste and adjust seasonings, adding thyme, salt, pepper as desired. Add more broth if needed to desired consistency.