Connecting two arduinos for seperate purposes

For my 4th year project, we have an ECG heart rate monitor so the sensors are connected to a front end circuit, then the circuit is connected to the Arduino that transfers the data to a mobile phone app (android) which transfers the data to a cloud.

Ideally we wanted to use one Arduino to control everything but this is not possible. After some research I found that the Adafruit RGB LCD is not compatible with the Arduino Due.

Is there a way to connect two arduinos together so that the Arduino Uno controls the LCD and the Arduino Due controls the data transfer and receive?

The LCD has a simple menu woth two options that controls whether or not data is being accepted to the Arduino Due.

You can have them talk to eachother over serial, or make one of them an I2C slave...

But I'd be inclined to just get a LCD that works with the Due...

Do you know of any LCD shields that are similar to the Adafruit RGB LCD that are compatible with the Due?

Also, how can I make one an I2C slave?

use arduino yun, it can post directly to the cloud