It's pretty much the same as a nominal bond, except cash flows need to be inflated. For example, here's the forward pricing formula for a Canadian-style linker, assuming one interim coupon payments:
$$ \bigl(F(t_f) + AI_{t_f}\bigr) \frac{I(t_f)}{I_\text{base}} = (P + AI_{t_s})\cdot \frac{I(t_s)}{I_\text{base}}\cdot (1 + r \cdot t_f) - c\cdot \frac{I(t_c)}{I_\text{base}}\cdot\bigl(1 + r\cdot (t_f - t_c)\bigr), $$
where $t_f$ represents the forward settlement date, $t_s$ is the spot settlement date, $t_c$ is the coupon date, and $I(t)$ is the index ratio for time $t$.
Note that if all the index ratio terms are removed, you've got the nominal bond forward pricing formula.
If the indexed ratios corresponding to the coupon date and forward settlement dates are not known, you'll need a projection curve to impute them.