You can use a CMOS-input rail-to-rail in/out op-amp (pick one suitable for 3.3V operation) and add another resistor from the non-inverting input to the positive supply to bias the op-amp. For example, all resistors 10K and select the capacitor to yield your desired frequency. Hopefully you have a Schmidt trigger input on the MCU interrupt input, because the rise and fall times may not be very fast, depending on the op-amp.
That resistor is required because without that it either will not oscillate (hang with the output low) or will give a very low duty cycle, depending on the output saturation voltage and the offset voltage at the inputs.
Note that you are using an op-amp as a comparator here, so some op-amps will be even more unsatisfactory than others.
Or just use a CMOS 555 such as TLC555.