  In broad classes of inflationary models the period of accelerated expansion
is followed by fragmentation of the inflaton scalar field into localized,
long-lived and massive oscillon excitations. We demonstrate that
matter-dominance of oscillons, followed by their rapid decay, significantly
enhances the primordial gravitational wave (GW) spectrum. These
oscillon-induced GWs, sourced by second-order perturbations, are distinct and
could be orders of magnitude lower in frequency than the previously considered
GWs associated with oscillon formation. We show that detectable
oscillon-induced GW signatures establish direct tests independent from cosmic
microwave background radiation (CMB) for regions of parameter space of
monodromy, logarithmic and pure natural (plateau) potential classes of
inflationary models, among others. We demonstrate that oscillon-induced GWs in
a model based on pure natural inflation could be directly observable with the
Einstein Telescope, Cosmic Explorer and DECIGO. These signatures offer a new
route for probing the underlying inflationary physics.
