LCD suggestions

Can someone suggest a small lcd screen ( 3" x 2" ish) which will work with both Arduino teensy and a Beaglebone Black? Separate projects but want to same product for both. Hopefully supported with libraries?

You are going to be looking for an SPI interface probably, if you want to use it on both boards. That will severely limit the update frequency on the display.

I suggest you search on Aliexpress. You will find a lot of displays there.
I would suggest keeping the resolution as low as you can live with.
Find one that has a very high SPI bus clock speed, you are going to be writing a lot of data.

Something like this perhaps. 3.5" LCD display 320x480

The displays usually have a flexi ribbon cable, so make sure you get one with an interface board of some kind.

Look at LVGL for a small lightweight graphics library. There are probably others. I have used LVGL on a framebuffer display, but pretty sure it will also work on an SPI type displays. You might need to write some code to support your chosen display, or at least modify an existing driver.