The best is always to communicate with your housemates. Try to be calm and tell them that the smell is making you nauseous. If there's a kitchen fan, politely ask them if they can please turn it on before they start cooking.
If possible, open the windows for at least a few minutes after they're done cooking to clear the air.
You should also try to contain the smell and distance yourself from its source. If the kitchen has a door, make sure it's closed. While they're cooking, try go to another room as far away as possible. Shut the door to your room too, and try to make it air-tight by putting a towel under the door.
Other than that, here's a few things you can do to overpower the smell
Produce Fresh Steam
Cut a lemon into thin slices and boil it in a big pot of water.
Optionally, add spices to the water for a potpourri scent: cloves, allspice, nutmeg, cinnamon, etc
Optionally, add essential oils to the water: lavender and rose are nice. This is also known as a steam diffuser.
Burn some incense or a scented candle.
Even just lighting a match and blowing it out may help because the resulting smoke is powerful.
Cook smelly vegan food
You may be able to mask the smell by cooking something yourself. Many vegan dishes can smell very strong, such as:
- Indian Curry
- Roasted Veggies
- (Deep) Fried Falafel
I wouldn't recommend it, but many consumers buy chemicals under-pressure cans and spray them. Popular brands are Fabreeze, Lysol, etc.