The turkey is going to be quite happy with the slightly lower temp - you will need a bit more time, but I'd guestimate 1/2 hour tops should be ok. This is another occasion to repeat our all important:
Use a thermomenter to determine doneness of your roast, not a timer!
The lasagna shouldn't be a problem either - I'm surprised at the long baking time anyway. Again, perhaps another 1/2 hour should be sufficient, if necessary at all.
Just note that at 350F / 175C your dishes might be browning a little less that you'd expect at 400F / 205C. Consider using the broiler when they are almost done to crisp them up a bit.